SUMMARY This project of the ICEMR focuses on the ecology of Anopheles malaria vector populations in Mali, West Africa, where, as in most African countries, current vector control tools used inside houses are not sufficient to achieve successful malaria control and local elimination. A better understanding of malaria vector and transmission ecology is needed. Research on malaria vectors is typically done in villages because this is where mosquitoes blood-feed on humans and transmit malaria parasites. Much less is known about how the ecology of vectors beyond the periphery of villages affects transmission. Key gaps in outside-village ecology that represent a major void in the understanding of transmission dynamics include: 1) sources and survival strategies of vector populations during the long dry season; 2) how vector survival and transmission potential are influenced by local environmental resources used for resting and sugar feeding; and 3) how recently- discovered natural infections of Wolbachia in anopheline mosquitoes may impact transmission. Therefore, the goal of this project is to investigate important neglected aspects of malaria vector and transmission field ecology at four sites in Mali, representing three major eco-zones that span the sub-Saharan Sahel region. Study sites are already well characterized with respect to vector populations, seasonal Plasmodium falciparum transmission, and malaria epidemiology. This project, which builds on extensive preliminary studies in Mali, includes three specific aims: 1) Evaluate how malaria vectors use limited natural and often cryptic habitats as refugia during the dry season and how these habitats serve as the source for population expansion with the onset of rains; 2) Determine how local environmental resources used for vector resting and sugar-feeding behavior impact malaria parasite transmission dynamics; and 3) Investigate the prevalence of Wolbachia and Plasmodium falciparum parasites in natural populations of the Anopheles gambiae complex in different ecological settings and experimentally test how Wolbachia affects vector competence. Innovative aspects include: First, preliminary results demonstrating isolated refugia along the River Niger, where during the dry season high densities of Anopheles gambiae complex mosquitoes exist and actually feed predominantly on birds, gives confidence that an integrated approach (ground searches, camera mounted drones, and satellite imagery) can be used to identify and define cryptic dry season habitats that are sources of vector populations during the dry season. Second, this is the first study to address the question of how vector sugar-feeding and resting specifically on invasive and agricultural plants affects transmission. Third, this is the first longitudinal ecological study of Wolbachia infecting malaria vector populations in Africa, and the first to examine how Wolbachia infections impact vector competence. New insights how on vector ecology impacts transmission in three eco-zones in Mali will provide field-based evidence needed for understanding how to overcome major barriers to malaria elimination in West Africa. !